Patent GB-846630-A (GB)
Title: Improvements relating to metal storage tanks for liquids
IPC: E04H7/06
Filed: 1958-07-22
Abstract: 846,630. Tanks. WIGGINS, J. H. July 22, 1958, No. 23543/58. Class 69 (1). In a storage tank of the suspension roof type having an outer side wall 10, a centre support 12, and a double suspension roof 13 comprising an outer roof portion 13b of predesigned shape sloping downwardly and inwardly from the side wall 10 and an inner roof portion 13a of pre-designed shape of double curvature, the roof portions 13a, 13b being joined to form an annular drain trough 16 including the lowest circle 86 (Fig. 3) of the roof, an erection frame for the roof comprises an outer portion 37 attached to the side wall 10 and extending inwardly therefrom and a limber inner portion 38 attached to the outer portion and to the centre support 12 and means for fixing the position of the lowest circle of the roof formed at the junctions of the erection frame portions 37, 38. The erection frame comprises a series of radial tension members for supporting roof plates. Each member consists of an outer part 21a and an inner part 21b hinged at 22 (Fig. 6). The portion 21a is hinged at 23 to the side wall 10 of the tank and the portion 21b is hinged at 24 to the centre support 12. A weight 35 is suspended from the hinge 22 to apply a downward force which pulls the two parts 21a, 21b into two different catenaries. Alternatively, a turnbuckle may be connected between the hinge point 22 and the bottom wall 11 of the tank (Fig. 7, not shown). In a further modification (Fig. 8) the radial tension member consists of a stiff straight beam 30 forming the outer portion and a limber tension member 21b. A turnbuckle 29 is applied between the inner member 21b and the central support 12. As the plates are laid on the radial tension member the dimension a of the hinge point 22 at the lowest circle tends to change very little. The dimension b does not change at all. This is because as the load is applied to the member 21a, it shortens the side wall 10 and moves it inwardly very slightly and this tends to lower the hinge point 22. As the plate load is applied to the inner portion 21b it tends to assume a smaller radius and tends to raise the point B. The point B is lowered by the tension in the inner portion 21b. The three effects tend to balance and have a very small effect on the dimension a. Any such change is compensated for by increasing the weight 35 or increasing the tension in the turnbuckle. As shown in Fig. 3, outer beams 37 are fastened to inner bars 38 by a pivotal member 43. A downward pull is exerted on the beams 37 by bracing rods 81 provided with turnbuckles 82. The limber bars 38 are connected by adjustable eye bolts 61 to a frustum plate 53 at the centre of the tank so that the erection frame can be pre-stressed to any desired extent and the position of the lowest circle 86 can be definitely fixed. The plates are first laid near the drain 17 (Fig. 1) in a complete ring to maintain the roof load balance. A preliminary tack welding is used to hold the plates in place. The radial tension members 81 may be adjusted from time to time to maintain the designed shape of the roof. When all the plates have been laid they are welded together and the erection frame is removed.